Centimeter-level High-strength Iron-based Bulk Amorphous Alloy and Novel Copper Mold Casting Method Thereof

ABSTRACT

The invention discloses a centimeter-level high-strength iron-based bulk amorphous alloy and novel copper mold casting method thereof; the molecular formula thereof is Fe44-xCo6Cr15Mo14C15B6Tmx, wherein x represents the atomic percent of corresponding alloy elements and 0≤x≤6; the novel copper mold casting method comprising: directly cooling a copper mold with cooling water under negative pressure through electric arc melting to obtain an amorphous alloy ingot; the alloy has the remarkable characteristics of high amorphous forming ability, high strength and high hardness, by the conventional casting, the maximum critical diameter can be 10 mm, the highest strength can be 4295 Mpa, and the highest Vickers hardness can be 1220 Hv; meanwhile, the alloy has obvious spinning glass behavior at low temperature; the preparation method has low cooling rate, is free from the limitation of mold diameter, and can directly obtain the amorphous alloy ingot, the cost is reduced, and the maximum diameter of the amorphous alloy ingot is 16.52 mm; and by the preparation method, the amorphous forming ability of the bulk amorphous alloy can be determined more accurately.

TECHNOLOGY FIELD

The invention relates to amorphous alloy and preparation method thereof, in particular to a centimeter-level high-strength iron-based bulk amorphous alloy and a novel copper mold casting method.

BACKGROUND ART

Amorphous alloy material is a novel material with disordered structure, due to the structural difference, it has many unique properties in terms of mechanics, magnetism, thermodynamics, etc. compared with crystalline metal materials. Fe-based amorphous alloys are a type of amorphous alloy systems in which the Fe atom accounts for the major proportion of the atomic percent of the component, many excellent properties thereof are given by the special structure of the Fe-bases metallic glass, such as high electrical resistivity, high magnetic conductivity and low loss rate, the Fe-based amorphous alloys are excellent soft magnetic material, and because of the excellent soft magnetic properties and price advantage, the discovery thereof has aroused great research interest from materials scientists, and has triggered a worldwide wave of research on Fe-based amorphous alloys.

The rich and diverse physical and chemical properties of rare earth elements brought about by special electronic and atomic structures have been applied to all aspects of science and technology. Especially in the development and application of new functional materials (light-emitting materials, magnetic materials, etc.), rare earth elements have become indispensable raw materials. However, unlike ordinary metals, rare earths are rarely used directly as metallic materials due to higher costs and easy oxidation. The rare earth elements are commonly used in combination with other elements to form new materials, which not only overcomes the shortcomings of the rare earth elements themselves, such as poor stability, also allows their rich and colorful properties to be fully utilized. A variety of new rare earth materials with excellent electrical, magnetic and optical properties have been proved to be the foundation of the high-tech dream. Simultaneously, the progress of society and the development of high technology have put forward higher requirements for materials, therefore, it is of great significance to develop materials with better performance based on the improvement of prior new rare earth materials. Studies have shown that amorphous alloys containing rare earth elements can have good amorphous forming ability, and also exhibit rich and unique physical, chemical, and mechanical properties. They are not only ideal objects for basic scientific research, but also have good application prospects.

One of the constraints that limit the application of Fe-based bulk amorphous alloys is their amorphous forming ability, the rare earth doping makes some systems have better amorphous forming ability, however, due to the volatile and loss of rare earth elements in the actual melting process, the prior rare-earth-doped amorphous alloy system with high amorphous forming ability requires a fixed proportion of the corresponding rare earth components, which is difficult for industrial applications. In the preparation method, the casting method for the amorphous alloy with high amorphous forming ability is highly dependent on the mold, and the preparation cost is relatively high.

SUMMARY OF THE INVENTION

The invention aims to provide a centimeter-level high-strength iron-based bulk amorphous alloy and a novel copper mold casting method, to solve the problems that the prior Fe-based amorphous alloy has poor amorphous forming ability, a narrow range of rare earth doping, and low efficiency; and that the existing casting method is highly dependent on a mold and has a high cost.

In order to achieve above objects, the invention adopts following technical schemes:

A centimeter-level high-strength Fe-based bulk amorphous alloy, the molecular formula thereof is Fe_(44-x)Co₆Cr₁₅Mo₁₄C₁₅B₆Tm_(x), wherein 0≤x≤6, and x represents the atomic percent of rare earth element Tm.

As an improvement of the invention, the structure of the Fe-based bulk amorphous alloy is fully amorphous structure, and critical diameter thereof is 2-10 mm.

As an improvement of the invention, the glass-transition temperature Tg thereof is 834-903K, the crystallization temperature Tx thereof is 895-959K, the supercooled liquid region ΔT(Tx-Tg) is 56-71K.

As an improvement of the invention, Vickers hardness Hv thereof is 1150-1220, the breaking strength of thereof is 2434-4295 Mpa.

As an improvement of the invention, the Fe-based bulk amorphous alloy has obvious spinning glass behavior at low temperature (0-30K), there is obvious bifurcation between the zero field-cooling curve (ZFC) and field-cooling curve (FC) in the DC magnetization curve, the freezing temperature Tf<2-12K and the Curie temperature TC is 21.5-27.7K.

As an improvement of the invention, a copper mold casting method for the centimeter-level high-strength Fe-based bulk amorphous alloy, comprising following steps:

(1) according to the atomic percent of the molecular formula, weighting Fe, Co, Cr, Mo₃C, FeC, C, B and Tm with a purity of not less than 99 wt. %, respectively;

(2) Mixing the weighted Fe, Co, Mo₃C, FeC, C, B and Tm, putting them in induction melting quartz tube and closing chamber, when the vacuum degree is below 5×10⁻³ Pa, filing inert gas therein and induction melting, heat-keeping for 10 minutes after melting raw materials, thereafter cutting off the current, and after preliminary cooling, taking out preliminary fused master alloy ingot;

(3) putting the preliminary fused master alloy ingot and rare earth element Tm into arc-melting furnace and closing chamber, when the vacuum degree is below 5×10⁻³ Pa, filing inert gas therein and melting at pressure of 3-7 x10⁴ Pa, after the raw materials are melted, continuously melting for 3-10 minutes, and then stopping heating, cooling the alloy to solidified and turning over, repeating the melting for 3-6 times, an alloy ingot with uniform composition is obtained;

(4) after removing the surface impurities of the alloy ingot and cleaning it, breaking the alloy ingot into small pieces, taking small pieces of alloy ingot and putting into copper crucible of the copper mold suction casting equipment, when the vacuum degree is below 5×10⁻³ Pa, filing inert gas therein to 3-7×10⁴ Pa, melting the alloy pieces by arc-melting, the internal and external air pressure difference of the copper mold suction casting moulding chamber is 0.05 Mpa, and sucking the molten alloy liquid into the copper mold, a Fe-base bulk amorphous alloy with high amorphous forming ability is obtained.

By adopting above technical schemes, the invention has following advantageous effects compared with prior art:

Fe, Cr, Mo, C, and B in the Fe-based bulk amorphous alloy in the invention are components of amorphous steel, the addition of Tm changes the order of atomic sizes in the system, and generates new atomic pairs with negative mixing, making it more consistent with the three empirical principles of amorphous formation, simultaneously, the rare earth element Tm can effectively bond the triangular prism local atomic configuration in the amorphous alloy system, thereby improving thermal stability and amorphous forming ability thereof, the addition of the rare earth element Tm in the composition of the invention at a percentage of 2-4 atoms can guarantee better amorphous forming ability, and provide greater fault tolerance for industrial applications. The novel copper mold casting method in the invention, can prepare bulk amorphous alloy ingots under natural water cooling conditions, and reduces the dependence on suction molds and reduces costs on the basis of traditional copper mold suction casting equipment, provides a new preparation method for amorphous alloy system with crystal forming ability, which has practical significance for industrial preparation.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

FIG. 1 is an XRD pattern of a critical size Fe-based bulk amorphous alloy prepared in in embodiment 1;

FIG. 2 an XRD pattern of Fe-based bulk amorphous alloy bar in 10 mm containing rare earth element Tm prepared in embodiment 1;

FIG. 3 is a DSC pattern of Fe-based bulk amorphous alloy prepared in embodiment 1;

FIG. 4 a stress-strain curve of Fe-based bulk amorphous alloy prepared in embodiment 1;

FIG. 5 is a DC magnetization curve of Fe-based bulk amorphous alloy prepared in embodiment 1;

FIG. 6 is an integral curve of FC curve magnetization intensity against temperature of Fe-based bulk amorphous alloy prepared in embodiment 1;

FIG. 7 is DC magnetization difference curve of Fe-based bulk amorphous alloy prepared in embodiment 1;

FIG. 8 is an integral curve of DC magnetization difference against temperature of Fe-based bulk amorphous alloy prepared in embodiment 1;

FIG. 9 is an XRD pattern of Fe-based bulk amorphous alloy prepared in embodiment 2;

FIG. 10 is a morphological photograph of Fe-based bulk amorphous alloy prepared in embodiment 2.

FIG. 11 is a schematic structural diagram of Fe-based bulk amorphous alloy copper mold casting equipment of embodiment 3.

SPECIFIC DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is further described below with reference to accompanying drawings.

Embodiment 1

In the embodiment, a centimeter-level high-strength Fe-based bulk amorphous alloy, the molecular formula thereof is Fe_(44-x)Co₆Cr₁₅Mo₁₄C₁₅B₆Tm_(x), wherein x=0, 2, 4, 6, the diameter thereof is 2 mm, 10 mm, 10 mm, 2 mm respectively, and the preparation method thereof is as follows:

(1) according to the atomic percent of the molecular formula Fe₄₄Co₆Cr₁₅Mo₁₄C₁₅B₆, Fe₄₂Co₆Cr₁₅Mo₁₄C₁₅B₆Tm₂, Fe₄₀Co₆Cr₁₅Mo₁₄C₁₅B₆Tm₄, Fe₃₈Co₆Cr₁₅Mo₁₄C₁₅B₆Tm₆, weighting Fe, Co, Cr, Mo₃C, FeC, C, B and Tm with a purity of not less than 99 wt. %, respectively;

(2) mixing weighted Fe, Co, Cr, Mo₃C, FeC, C, B and Tm in step 1, putting them in induction melting quartz tube and closing chamber, when the vacuum degree is below 5×10⁻³ Pa, filing inert gas therein to protect and induction melting, heat-keeping for 10 minutes after melting raw materials, thereafter cutting off the current, and taking out preliminary fused master alloy ingot after preliminary cooling;

(3) putting the preliminary fused master alloy ingot obtained in step 2 and rare earth element Tm into arc-melting furnace and closing chamber, when the vacuum degree is below 5×10-3 Pa, filing inert gas therein and melting at pressure of 3-7×10⁴ Pa, after the raw materials are melted, continuously melting for 5 minutes, and then stopping heating, cooling the alloy to solidified with the cooling of the crucible and turning over, repeating the melting for 5 times, an alloy ingot with uniform composition is obtained;

(4) after removing the surface impurities of the alloy ingot obtained in step 3 and cleaning it, breaking the alloy ingot into small pieces, taking small pieces of alloy ingot and putting into copper crucible of the copper mold suction casting equipment, when the vacuum degree is below 5×10⁻³ Pa, filing inert gas therein to 3-7×10⁴ Pa, melting the alloy pieces by arc-melting, the internal and external air pressure difference of the copper mold suction casting moulding chamber is 0.05 Mpa;

(5) under the protection of inert gas, turning on the power supply arc striking and gradually increasing the current intensity until the alloy pieces are melted, and sucking the molten alloy liquid into the copper mold in corresponding diameter by using pressure difference, a Fe-base bulk amorphous alloy with high amorphous forming ability is obtained.

As shown in FIG. 1, The XRD patterns, testing by D8 Advance polycrystalline X-ray diffractometer, of Fe-based bulk amorphous alloy prepared in step 5 with high amorphous forming ability, are all diffuse scattering peaks, indicating that the bulk alloy bar is all the same amorphous structure when the diameter thereof is 2 mm, 10 mm, 10 mm, 2 mm, respectively. As shown in FIG. 2, XRD analysis was performed on 10 mm bars of three alloys containing rare earth element Tm, it can be seen that when the rare earth element Tm increases from 4 atomic percent to 6 atomic percent, the alloy easily precipitates various crystal phases including (FeCo) C, α-Fe, BC and CrMo.

The DSC curve (FIG. 3) of Fe-based bulk amorphous alloy prepared in step 5 is measured by using an NETZSCH DSC 404 F3 differential scanning calorimeter, the temperature rise rate is 40 Kelvin/minute, and according to DSC curve, it is obtained that when x=0/2/4/6, the glass transition temperatures Tg of the amorphous alloy are respectively 834K, 850K, 872K and 903K, the initial crystallization temperatures Tx are respectively 895K, 939K, 942K and 959K, and the supercooled liquid region widths ΔT are respectively 61K, 71K, 70K, 56K, as shown in Table 1.

TABLE 1 Properties of prepared amorphous alloys Thermodynamic Magnetic Mechanical Critical Parameter Property Property Serial Number Alloy Composition Diameter (mm) T_(g)/K T

/K Δ T/K T

/K T

/K

f/Mpa Hv Embodiment 1-1 Fe₄₄Co

Cr₁₅Mo₁₄C₁₅B₆ 2 834 895 61 <2 27.7 3013 1170 Embodiment 1-2 Fe

Co

C

Mo

C₁₅B₆Tm₂ 10 850 939 71 8.0 23.0 4295 1220 Embodiment 1-3 Fe

Co

Cr

Mo

C

B

Tm₄ 10 872 942 70 10.0 22.3 3048 1193 Embodiment 1-4 Fe

Co

Cr

Mo

C₁₅B₆Tm

2 903 959 56 12.0 21.5 2434 1150

indicates data missing or illegible when filed

The hardness and strength of the alloy are respectively tested by FM-700 microhardness tester and CMT5105 electronic universal testing machine. As shown in Table 1, when x=0/2/4/6, the Vickers hardness of the alloy is respectively 1170, 1220, 1193, 1150, and according to the compressive stress-strain curve shown in FIG. 4, the breaking strength thereof is respectively 3013 Mpa, 4295 Mpa, 3048 Mpa, 2434 Mpa, higher hardness indicates good wear-resisting property, and the breaking strength is much higher than that of super-strength steel, indicating that the bulk amorphous alloy system has good mechanical property.

The SQUID-VSM type magnetic property measurement system (MPMS) is used to measure the DC magnetization curve of the alloy, and the applied measurement magnetic field is 200Oe. As shown in FIG. 5, with the decrease of the temperature, the magnetization intensity gradually increases from around zero, indicating that the magnetic state of these alloy samples changes from paramagnetic to ferromagnetic at high temperatures. When the temperature of the alloy system continues to decrease, the magnetization intensity appears a peak at about 10-15K, and then gradually decreases, the magnetization curve with field cooling (FC) and the magnetization curve with zero-field cooling (ZFC) are bifurcated at about 3-10K from the state where they basically coincided before, which can be concluded that the Fe-based bulk amorphous system has spinning glass behavior at low temperature. When the temperature continues to decrease, the ZFC curve starts to decrease rapidly with the temperature drop, simultaneously, the FC curve only decreases slowly, because the ZFC curve can show the magnetic moment change of irregularly frozen magnetic ions, and in the process of the temperature decrease, the magnetic moment in the sample is frozen in an irregularly oriented state, thereby the macroscopic magnetization intensity is almost zero; The FC curve mainly shows the magnetic moment of orientedly inducted magnetic ions in an applied field, thereby the magnetic moment arrangement show a certain regularity, and macroscopic magnetization intensity displayed outside is not zero. FIG. 6 is an integral curve of FC curve magnetization intensity against temperature in DC magnetization curve, the temperature corresponding to the point that the absolute maximum value of the minimum value in FIG. 6 against slope of the magnetization curve, is regarded as Curie temperature (Tc). FIG. 7 is a difference curve between the FC curve and the ZFC curve, it can be seen that the spinning glass behavior is most obvious when x=2 in the Fe-based amorphous alloy system, FIG. 8 is an integral curve of DC magnetization difference against temperature, the temperature corresponding to the point that the absolute maximum value of the minimum value in FIG. 8 against slope of the integral curve, is regarded as freezing temperature (Tf). When x=0/2/4/6, freezing temperature (Tf)<2K, 8.0K, 10.0K, 12.0K, the Curie temperature (Tc) is 27.7K, 23.0K, 22.3K, 21.5K, and as shown in Table 1, with the increase of the rare earth element Tm, the freezing temperature of the alloy gradually increases, and the Curie temperature of the alloy gradually decreases.

Embodiment 2

In the embodiment, a centimeter-level high-strength Fe-based bulk amorphous alloy, the molecular formula thereof is Fe₄₂Co₆Cr₁₅Mo₁₄C₁₅B₆Tm_(x), and the preparation method thereof is as follows:

(1) according to the atomic percent of the molecular formula Fe₄₂Co₆Cr₁₅Mo₁₄C₁₅B₆Tm₂, weighting Fe, Co, Cr, Mo₃C, FeC, C, B and Tm with a purity of not less than 99 wt. %, respectively;

(2) mixing weighted Fe, Co, Cr, Mo₃C, FeC, C, B and Tm in step 1, putting them in induction melting quartz tube and closing chamber, when the vacuum degree is below 5×10⁻³ Pa, filing inert gas therein to protect and induction melting, heat-keeping for 10 minutes after melting raw materials, thereafter cutting off the current, and taking out preliminary fused master alloy ingot after preliminary cooling;

(3) putting the preliminary fused master alloy ingot obtained in step 2 and rare earth element Tm into arc-melting furnace and closing chamber, when the vacuum degree is below 5×10⁻³ Pa, filing inert gas therein and melting at pressure of 3-7×10⁴ Pa, after the raw materials are melted, continuously melting for 5 minutes, and then stopping heating, cooling the alloy to solidified with the cooling of the crucible and turning over, repeating the melting for 5 times, an alloy ingot with uniform composition is obtained;

(4) after removing the surface impurities of the alloy ingot obtained in step 3 and cleaning it, breaking the alloy ingot into small pieces, taking small pieces of alloy ingot and putting into copper crucible of the copper mold suction casting equipment, when the vacuum degree is below 5×10⁻³ Pa, filing inert gas therein to 3-7×10⁴ Pa, melting the alloy pieces by arc-melting, cutting off the current of tungsten electrode, the internal and external air pressure difference of the copper mold suction casting moulding chamber is 0.05 Mpa, the molten alloy is pressed against a copper mold with water cooling under pressure difference to achieve maximum contact, and after cooling, an amorphous alloy ingot is obtained.

The XRD patterns, testing by D8 Advance polycrystalline X-ray diffractometer, of metallic glass alloy prepared in step 4, are diffuse scattering peaks, as shown in FIG. 9, XRD analysis was performed on 10 mm bars of three alloys containing rare earth element Tm, it can be seen that when the rare earth element Tm increases from 4 atomic percent to 6 atomic percent, the alloy easily precipitates various crystal phases including (FeCo) C, α-Fe, BC and CrMo.

Embodiment 3

The copper mold suction casting equipment used for a novel amorphous alloy copper mold casting method of the invention, as shown in FIG. 11, comprising copper mold suction casting equipment body, wherein the copper mold suction casting equipment body comprises a chamber 2 and a copper mold 4 which are sequentially arranged from top to bottom, at least two copper crucibles 3 are arranged between the copper mold 4 and the chamber 2, an electrode 1 is arranged in the chamber 2 in a penetrating manner, the lower end of the electrode 1 is arranged in the copper crucibles 3, a suction casting mold chamber 7 communicated with the copper crucibles for suction casting is provided in the copper mold 4, the suction casting mold chamber 7 is arranged at the lower ends of the copper crucibles 3, a copper plug 6 is arranged in the suction casting mold chamber 7, water cooling devices 5 are both arranged on the left side and the right side of the suction casting mold chamber 7, and the water cooling devices 5 are arranged in the copper mold 4.

The chamber 2 is a vacuum electric arc furnace chamber, a plurality of copper crucibles 3 are arranged in the chamber, wherein at least one copper crucible 3 is a copper crucible for suction casting, the other copper crucibles are for melting, the tungsten electrode 1 penetrates through a furnace shell and extends into the copper crucible 3 of the chamber 2, and the copper crucible 3 for suction casting is put into alloy raw materials which are evenly melted according to the required component proportion.

The novel copper mold casting method uses copper plug 6 in the suction casting chamber mold chamber 7 for traditional cooper suction casting to prevent molten metal from flowing into the chamber 2 under negative pressure.

The above embodiments are merely preferred embodiments of the invention, and should not limit the invention, and the protect scope of the invention should be defined by the claims, and equivalents of technical features described in the claims are intended to be included in the scope of the invention, that is, equivalent modifications within the scope of the invention are also within the protect scope of the invention. 

1. A centimeter-level high-strength Fe-based bulk amorphous alloy, the molecular formula thereof is Fe_(44-x)Co₆Cr₁₅Mo₁₄C₁₅B₆Tm_(x), wherein 0≤x≤6, and x represents the atomic percent of rare earth element Tm.
 2. The centimeter-level high-strength Fe-based bulk amorphous alloy of claim 1, wherein the structure of the Fe-based bulk amorphous alloy is fully amorphous structure, and critical diameter thereof is 2-10 mm.
 3. The centimeter-level high-strength Fe-based bulk amorphous alloy of claim 1, wherein the glass-transition temperature Tg thereof is 834-903K, the crystallization temperature Tx thereof is 895-959K, the supercooled liquid region ΔT(Tx-Tg) is 56-71K.
 4. The centimeter-level high-strength Fe-based bulk amorphous alloy of claim 1, wherein Vickers hardness Hv thereof is 1150-1220, the breaking strength σf thereof is 2434-4295 Mpa.
 5. The centimeter-level high-strength Fe-based bulk amorphous alloy of claim 1, wherein the Fe-based bulk amorphous alloy has obvious spinning glass behavior at low temperature, there is obvious bifurcation between the zero field-cooling curve and field-cooling curve in the DC magnetization curve, the freezing temperature Tf<2-12K and the Curie temperature TC is 21.5-27.7K.
 6. A copper mold casting method for the centimeter-level high-strength Fe-based bulk amorphous alloy according to claims 1-5, comprising following steps: (1) according to the atomic percent of the molecular formula, weighting Fe, Co, Cr, Mo₃C, FeC, C, B and Tm with a purity of not less than 99 wt. %, respectively; (2) mixing weighted Fe, Co, Cr, Mo₃C, FeC, C, B and Tm, putting them in induction melting quartz tube and closing chamber, when the vacuum degree is below 5×10⁻³ Pa, filing inert gas therein and induction melting, heat-keeping for 10 minutes after melting raw materials, thereafter cutting off the current, and after preliminary cooling, taking out preliminary fused master alloy ingot; (3) putting the preliminary fused master alloy ingot and rare earth element Tm into arc-melting furnace and closing chamber, when the vacuum degree is below 5×10⁻³ Pa, filing inert gas therein and melting at pressure of 3-7 x10⁴ Pa, after the raw materials are melted, continuously melting for 3-10 minutes, and then stopping heating, cooling the alloy to solidified and turning over, repeating the melting for 3-6 times, an alloy ingot with uniform composition is obtained; after removing the surface impurities of the alloy ingot and cleaning it, breaking the alloy ingot into small pieces, taking small pieces of alloy ingot and putting into copper crucible of the copper mold suction casting equipment, when the vacuum degree is below 5×10⁻³ Pa, filing inert gas therein to 3-7×10⁴ Pa, melting the alloy pieces by arc-melting, the internal and external air pressure Difference of the copper mold suction casting moulding chamber is 0.05 Mpa, and sucking the molten alloy liquid into the copper mold, a Fe-base bulk amorphous alloy with high amorphous forming ability is obtained. 